Using a Chlamydomonas model system, we have established the occurrence of a number of basic meiotic processes at the molecular level by biophysico-chemical and genetic methods. These include: 1) the timing and mode of meiotic DNA replication; 2) the physical recombination pattern of chromosomal and organelle DNA; 3) the temporary occurrence of a meiotic-specific DNA component that may be responsible for the synaptic crossing-over process and 4) the induction of a meotic-specific enzyme. We have also made advances in the induction and control of meiotic cell division. However, much remains to be learned about the molecular mechanisms of meiosis, which is an integral part of the sexual reproductive process. With the results thus far obtained and the valuable insights and experience that we have gained during the past 26 months, we believe that we are near the threshold of resolving the molecular mechanisms of synaptic crossing-over. Therefore, in this proposal, we intend (1) to elucidate the mechanistic details of the crossing-over process and its inter-relationship with the synaptic structure of homologs and (2) to correlate the induction of meiotic-specific enzymes with the control of meiotic cell division and DNA recombination processes. Subsequent to these basic studies we plan to study whether the occurrence of meiotic cell division and the frequency of synaptic crossing-over in meiosis can be experimentally controlled not only in this highly suitable model system but also in other higher organisms.